Magnetically inductive flowmeter

ABSTRACT

The invention relates to a magnetically inductive flowmeter ( 1 ) comprising:
     a measuring tube ( 10 ) having a measuring tube axis ( 11 ) and a measuring tube wall ( 12 );   a magnet system ( 20 ) for producing a magnetic field, which extends perpendicularly to the measuring tube axis;   at least one pair of measuring electrodes ( 30 ) for sensing an electrical voltage induced in the medium by the magnetic field,   an electronic measuring/operating circuit ( 40 ) for operating the magnet system and the measuring electrodes,   wherein the magnet system ( 20 ) comprises:   a coil system ( 21 ) having at least one coil ( 21.1 ) having a coil core ( 21.2 ); two pole shoes ( 22 );   wherein the coil system ( 21 ) has a means for field guide-back ( 21.3 ), characterized in that   a tangential fraction of the magnetic field in the coil relative to the measuring tube axis amounts to at least 90% of the total magnetic field,   wherein the means for field guide-back ( 21.3 ) has at least one guide-back part ( 21.4 ), which extends through at least one coil and forms the coil core ( 21.2 ) of the at least one coil ( 21.1 ).

The invention relates to a magnetically inductive flowmeter for measuring volume flow or flow velocity of a medium flowing through a measuring tube.

Magnetically inductive flowmeters are based on measuring an electrical voltage induced in an electrically conductive medium by a magnetic field, which electrical voltage is linearly dependent on the applied magnetic field and on the volume flow of the medium through the measuring tube.

The magnetic field is usually produced by means of a magnet system having at least one coil. Thus, for example, DE102015122664A1 discloses a magnetically inductive flowmeter, in the case of which a magnetic field perpendicular to a measuring tube axis is produced by means of two coils, wherein the coil axes are perpendicular to the measuring tube axis. The magnetic field outside of the measuring tube and outside of the coils is led between the two coils by means of a field guide, wherein a magnetic connecting between coil core of a coil and field guide as well as between measuring tube and coil core is produced, in each case, by means of a pole shoe. Since each connection represents an interruption of the magnetic flux, such degrades performance of the flowmeter. Moreover, the concentration of the production of the magnetic field in the region of the coils means that many turns of a coil wire must be applied in a narrow spatial region. This leads to a lessened heat emission and to a waste of costly raw materials, since many turns in a narrow spatial region can only be accomplished by using a large number of winding layers.

An object of the invention is, consequently, a magnetically inductive flowmeter, which at least lessens at least one of the aforementioned disadvantages.

The object is achieved by a magnetically inductive flowmeter as defined in independent claim 1.

A magnetically inductive flowmeter of the invention for measuring volume flow or flow velocity of a medium flowing through a measuring tube comprises:

the measuring tube having a measuring tube axis and a measuring tube wall;

a magnet system for producing a magnetic field, which extends perpendicularly to the measuring tube axis, wherein the magnet system is placed on an outside of the measuring tube;

at least one pair of measuring electrodes, which are coupled capacitively or galvanically with the medium located in the measuring tube, wherein the measuring electrodes are adapted to sense an electrical voltage induced in the medium by the magnetic field, wherein a first measuring electrode of the pair of measuring electrodes is arranged on a first side of the measuring tube and a second measuring electrode of the pair of measuring electrodes is arranged on a second side of the measuring tube;

an electronic measuring/operating circuit for operating the magnet system and the measuring electrodes as well as for providing measured values of flow,

wherein the magnet system comprises:

a coil system having at least one coil having a coil core;

two pole shoes, which are arranged on opposite sides of the measuring tube, wherein the pole shoes are adapted to transfer the magnetic field produced by the coil system into the measuring tube as well as to receive the magnetic field, which has passed through the measuring tube, and to lead the magnetic field back to the coil system;

wherein the coil system has a means for field guide-back, which is adapted to lead the magnetic field outside of the measuring tube between the pole shoes,

characterized in that

a tangential fraction of the magnetic field in the coil relative to the measuring tube axis amounts to at least 80% and especially at least 90% of the total magnetic field,

wherein the means for field guide-back has at least one guide-back part, which extends through at least one coil and forms the coil core of the at least one coil.

A measuring tube can be described by means of a cylindrically symmetrical coordinate system comprising a radial coordinate, an axial coordinate and a tangential coordinate. The tangential fraction of the magnetic field concerns, thus, the part of the magnetic field, which is oriented along the tangential coordinate. Tangential orientation of the at least one coil on the measuring tube and extension of the field guide-back through the coil eliminates a transition at each pole shoe between a field guide and a coil core by combining the field guide-back and at least one coil core into one unit, in order to eliminate a connecting of two components. In this way, a magnetic resistance of the magnet system is reduced. A minimum fraction of 80% of the tangential fraction to the total magnetic field can leave room for an easy axial or radial orientation of the coil along the associated guide-back part.

The pole shoes are, in each case, produced preferably of at least one non-grain oriented sheet metal piece and lie against the measuring tube.

In an embodiment, the guide-back part comprises at least one ply of electrical sheet metal, which meets the requirements of the standard, DIN EN 10106 edition 2007-11, or wherein the electrical sheet metal is especially grain oriented and meets the requirements of the standard, DIN EN 10107 edition 2005-10, wherein the grain orientation is in parallel with the magnetic flux in the guide-back part.

A grain orientation of a magnetically conductive material provides a non-isotropic magnetic conductivity, wherein a magnetic resistance of the material along the grain orientation is minimum. By orienting the grain orientation along the magnetic flux of the magnetic field in the guide-back, thus, the magnetic resistance of the magnet system is lessened.

In an embodiment, the coil has at most 15 winding plies and especially at most 10 winding plies and preferably at most 5 winding plies.

In this way, use of raw materials applied for winding the coil, such as, for example, copper or silver, can be minimized. Moreover, this lessens the danger of an overheating of the coils, which results from high current flow in the coil and many winding layers.

In an embodiment, a length of the coil along its longitudinal axis subtends an angle α of at least 2 degree, and especially at least 5 degree and preferably at least 10 degree about the measuring tube axis. A greater length contributes to reducing the number of winding plies.

In an embodiment, there is arranged on the first side and the second side of the measuring tube, in each case, at least one coil with an associated guide-back part.

A two-sided arrangement of coils and associated guide-back parts contributes to an equally formed magnetic flux in the pole shoes, this leading to a spatially homogeneous distribution of the magnetic field in the region of the measuring electrodes.

In an embodiment, the measuring tube has extending along the measuring tube axis two far regions, a central region and two intermediate regions, wherein, in each case, an intermediate region is arranged between a far region and the central region,

wherein the measuring tube has in its far regions, in each case, a flange and a collar, which flanges are adapted to be connected to a pipeline,

wherein the at least one measuring electrode pair is arranged in the central region.

In an embodiment, the pole shoes and/or guide-back parts and/or coils are, in each case, arranged symmetrically relative to a cross- and/or longitudinal section of the measuring tube.

By increasing a degree of symmetry of the magnet system, a spatial distribution of the magnetic field in the region of the measuring electrodes can be formed homogeneously.

In an embodiment, the pole shoes subtend in the central region an angle β_(M) of at least 40 degree and especially at least 80 degree and preferably at least 120 degree about the measuring tube axis, wherein the pole shoes are separated from one another by two gaps, wherein each gap subtends an angle γ of at least 5 degree and especially at least 10 degree and preferably at least 15 degree about the measuring tube axis.

In this way, the distribution of the magnetic field in the measuring tube can be adapted. The minimum extension of the gap between the pole shoes contributes to preventing a magnetic short circuit, in the case of which a magnetic flux in the measuring tube would be disturbed.

In an embodiment, the guide-back part is arranged in the central region and includes especially at least one feedthrough for contacting a measuring electrode and/or for grouting,

wherein the guide-back part extends through at least one coil, and preferably through two coils, wherein the at least two coils are arranged on opposite sides relative to the corresponding measuring electrode.

In an embodiment, the pole shoes subtend in the intermediate regions about the measuring tube axis, in each case, an angle β_(Z), which is less than the angle β_(M) by at least 30 degree and especially at least 40 degree and preferably at least 50 degree,

wherein the field guide-back has on the first side and/or second side at least two guide-back parts, which magnetically connect the pole shoes, in each case, in an intermediate region.

In an embodiment, the magnet system includes a shielding apparatus, which is adapted to minimize magnetic disturbing influences of the flanges and collars,

wherein the shielding apparatus has at least one shielding band, which at least partially surrounds the measuring tube, wherein the shielding band is arranged between a flange and the central region or on a side of the collar facing the central region,

wherein the shielding band is made of a magnetically conductive material,

wherein the shielding band is, for example, one piece or composed of a plurality of band portions.

This contributes to an increasing of a possible switching frequency of the magnet system as well as to longer measuring times, since magnetic disturbing influences caused by currents induced in the flanges and collars in the measuring electrode region fall faster under a critical limit.

In an embodiment, the shielding apparatus has two shielding bands, each of which is associated with a flange.

In an embodiment, the guide-back part has at least 5 and especially at least 10 and preferably at least 15 plies of electrical sheet metal. In this way, the magnetic conductivity of the guide-back part can be improved.

In an embodiment, the measuring tube has an inner diameter of at least 0.35 meters and especially at least 1 meters and preferably at least 1.5 meters.

Especially in the case of measuring tubes with large tube diameters, the invention provides great advantages as regards the performance of the flowmeter.

The invention will now be described based on examples of embodiments presented in the appended drawing, the figures of which show as follows:

FIG. 1 a typical magnetically inductive flowmeter according to the state of the art;

FIG. 2 a magnetically inductive flowmeter of the invention;

FIGS. 3 a) to c) schematic side views of alternative embodiments of a magnetically inductive flowmeter of the invention.

FIG. 1 shows a cross section of a known, magnetically inductive flowmeter, wherein the flowmeter includes a measuring tube 10, measuring electrodes 30, and a magnet system with, arranged on opposite sides of the measuring tube, two coils 21.1, each of which has a coil core 21.2, wherein, in each case, a pole shoe 22 is adapted to guide the magnetic field between measuring tube and coil and to form its spatial distribution in the measuring tube. The magnetic flux outside of the measuring tube between the measuring tube far sides of the coils is guided by means of a field guide-back. The magnetic flux is degraded at the transitions between field guide-back and coils, as well as between coil and pole shoe. Moreover, in order to embody the coil spatially compactly, a large number of winding layers of coil wire are necessary, which, however, is disadvantageous as regards consumption of coil wire and also problematic concerning possible overheating of the coil.

FIG. 2 shows in the form of a simplified cross-sectional drawing a schematic construction of an example of a magnetically inductive flowmeter 1 of the invention in a central region 10.1 of the measuring tube. The flowmeter 1 includes a measuring tube 10, a magnet system 20, a pair of measuring electrodes 30 arranged in the measuring tube, and an electronic measuring/operating circuit 40, which is adapted to operate the measuring electrodes 30 and the magnet system 20 as well as to provide measured values of flow. For illustrative reasons, electrical connections are shown between the measuring electrodes and the electronic measuring/operating circuit 40 and only between one coil and the electronic measuring/operating circuit 40. The magnet system 20 includes a coil system 21 and two pole shoes 22, which are adapted to conduct the magnetic field produced by the coil system between coil system 21 and measuring tube 10 and to determine the spatial distribution of the magnetic field in the measuring tube. The coil system includes four coils 21.1 with, in each case, a coil core 21.2, and a field guide-back 21.3 with two guide-back parts 21.4, which are arranged on opposite sides of the measuring tube and extend through, in each case, two coils 21.1 and, thus, form the coil cores 21.2 of the associated coils. The pole shoes have, in such case, in each case, a thin sheet metal piece, and lie other than shown in FIG. 2 against the measuring tube 10. The field guide-back 21.3 is, in such case, magnetically coupled with the pole shoes 22 in four contact areas K, wherein the guide-back parts 21.4 lie other than shown in FIG. 2 against the pole shoes. The deviating representation is, in such case, for the purpose of making the individual components of the magnetically inductive flowmeter recognizable. The provision of the guide-back parts 21.4 as coil cores 21.2 enables the coils to be oriented in the tangential direction of the measuring tube. This can enlarge a length of the coils along a coil axis and lessen the number of winding layers, this leading to a saving of material and at least reducing excess heating of the coil in measurement operation. The length of the coil along its longitudinal axis relative to the measuring tube axis 10.6 subtends an angle α of at least 2 degree, and especially at least 5 degree and preferably at least 10 degree. Additionally, due to the construction of the invention, the transition between a coil core and a guide-back part is omitted, since the guide-back parts assume the function of at least one coil core, whereby the magnetic resistance of the coil system is reduced.

For an advantageous spatial formation of the magnetic field in the region of the measuring electrodes 20, the pole shoes subtend in the central region 10.1 relative to the measuring tube axis 10.6 an angle β_(M) of at least 40 degree and especially at least 80 degree and preferably at least 120 degree, wherein the pole shoes are separated from one another by two gaps, wherein each gap has an angle γ of at least 5 degree and especially at least 10 degree and preferably at least 15 degree. The gaps are adapted to prevent a magnetic short circuit between the pole shoes.

The guide-back parts can have a feedthrough (not shown) for measuring electrode contacting.

A magnetically inductive flowmeter of the invention is not limited to four coils and two guide-back parts. A flowmeter of the invention can have n1 coils and n2 guide-back parts, wherein n1 and n2 are natural numbers and n2<n1+1.

FIGS. 3 a) to c) show schematic, side views of alternative examples of embodiments of a magnet system of a magnetically inductive flowmeter of the invention, wherein FIG. 3a ) has a measuring tube 10 with a magnet system 20 arranged thereon in a central region of the measuring tube 10.1, wherein the magnet system has on the shown side a coil system 21 with two pole shoes and a guide-back part 21.4 of a field guide-back 21.3. The field guide-back part includes in a central region a feedthrough 21.41 for a measuring electrode contacting. The measuring tube includes in far regions 10.3, in each case, a flange 10.5 and a collar 10.4, wherein the flanges are adapted to insert the flowmeter into a pipeline system, wherein the collars are adapted to be able to position a jacket around the measuring tube, wherein the jacket can have shielding sheet metal pieces, in order to shield the magnet system from external fields.

FIG. 3 b) shows a magnet system, which is symmetric relative to a measuring tube cross section, wherein the shown coil system in FIG. 3 a) is doubly embodied and symmetrically arranged relative to the cross section. In this way, the electrical connection of the measuring electrodes 30 to the electronic measuring/operating circuit can be embodied without a feedthrough 21.41 such as shown in FIG. 3a ). The flux of the magnetic field in the guide-back parts is, thus, not hindered. Alternatively, an option is, for example, to provide only one coil 21.1 per guide-back part 21.4.

FIG. 3 c) shows another opportunity for providing a magnet system of the invention, wherein the pole shoes subtend in the intermediate regions 10.2 a lesser angle relative to the measuring tube axis.

Common to the embodiments of the magnet systems shown in FIGS. 3a ) to 3 c) is as follows: The magnetic field produced by the coil system causes in the flanges 10.5 and in the collars 10.4 electrical currents, which, in turn, disturb the magnetic field in the region of the measuring electrodes and lessen the measuring power of the flowmeter. In order to lessen these disturbing influences, the magnet system includes a shielding apparatus 23 comprising two shielding bands 23.1, which are arranged on the coil system 21 facing sides of the collars, or flanges. The shielding bands comprise a magnetically conductive material and thereby lessen propagation of the disturbing influences to the measuring electrodes.

The magnet system includes on the side of the measuring tube opposite the shown side preferably at least one other coil and at least one other guide-back part, which advantageously are arranged symmetrically to the shown coils as well as to the guide-back parts relative to a longitudinal section of the measuring tube.

LIST OF REFERENCE CHARACTERS

-   1 magnetically inductive flowmeter -   10 measuring tube -   10.1 central region -   10.2 intermediate region -   10.3 far region -   10.4 collar -   10.5 flange -   11 measuring tube axis -   12 measuring tube wall -   20 magnet system -   21 coil system -   21.1 coil -   21.2 coil core -   21.3 field guide-back -   21.4 guide-back part -   21.41 feedthrough for measuring electrode contacting -   22 pole shoe -   23 shielding apparatus -   23.1 shielding band -   30 measuring electrodes -   31 first measuring electrode -   32 second measuring electrode -   40 electronic measuring/operating circuit 

1. Magnetically inductive flowmeter (1) for measuring volume flow or flow velocity of a medium flowing through a measuring tube (10), comprising: the measuring tube (10) having a measuring tube axis (11) and a measuring tube wall (12); a magnet system (20) for producing a magnetic field, which extends perpendicularly to the measuring tube axis, wherein the magnet system is placed on an outside of the measuring tube; at least one pair of measuring electrodes (30), which are coupled capacitively or galvanically with the medium located in the measuring tube, wherein the measuring electrodes are adapted to sense an electrical voltage induced in the medium by the magnetic field, wherein a first measuring electrode (31) of the pair of measuring electrodes is arranged on a first side of the measuring tube and a second measuring electrode (32) of the pair of measuring electrodes is arranged on a second side of the measuring tube; an electronic measuring/operating circuit (40) for operating the magnet system and the measuring electrodes, wherein the magnet system (20) comprises: a coil system (21) having at least one coil (21.1) having a coil core (21.2); two pole shoes (22), which are arranged on opposite sides of the measuring tube, wherein the pole shoes are adapted to transfer the magnetic field produced by the coil system into the measuring tube as well as to receive the magnetic field, which has passed through the measuring tube, and to lead the magnetic field back to the coil system; wherein the coil system (21) has a means for field guide-back (21.3), which is adapted to lead the magnetic field outside of the measuring tube between the pole shoes, characterized in that a tangential fraction of the magnetic field in the coil relative to the measuring tube axis amounts to at least 90% of the total magnetic field, wherein the means for field guide-back (21.3) has at least one guide-back part (21.4), which extends through at least one coil and forms the coil core (21.2) of the at least one coil (21.1).
 2. Flowmeter (1) as claimed in claim 1, wherein the guide-back part (21.4) has at least one ply of electrical sheet metal, which meets the requirements of the standard, DIN EN 10106 edition 2007-11, or wherein the electrical sheet metal is especially grain oriented and meets the requirements of the standard, DIN EN 10107 edition 2005-10, wherein the grain orientation is in parallel with the magnetic flux in the guide-back part.
 3. Flowmeter (1) as claimed in claim 1 or 2, wherein the coil (21.1) has at most 15 winding plies and especially at most 10 winding plies and preferably at most 5 winding plies.
 4. Flowmeter (1) as claimed in one of the previous claims, wherein a length of the coil along its longitudinal axis subtends an angle α of at least 2 degree, and especially at least 5 degree and preferably at least 10 degree about the measuring tube axis.
 5. Flowmeter (1) as claimed in one of the previous claims, wherein there is arranged on the first side and the second side of the measuring tube, in each case, at least one coil with an associated guide-back part.
 6. Flowmeter (1) as claimed in one of the previous claims, wherein the measuring tube (10) has extending along the measuring tube axis (11) two far regions (10.3), a central region (10.1) and two intermediate regions (10.2), wherein, in each case, an intermediate region is arranged between a far region and the central region, wherein the measuring tube has in its far regions, in each case, a flange (10.5) and a collar (10.4), which flanges are adapted to be connected to a pipeline, wherein the at least one measuring electrode pair is arranged in the central region.
 7. Flowmeter (1) as claimed in one of the previous claims, wherein the pole shoes (22) and/or guide-back parts (21.4) and/or coils (21.1) are, in each case, arranged symmetrically relative to a cross- and/or longitudinal section of the measuring tube.
 8. Flowmeter (1) as claimed in claim 7, wherein the pole shoes (22) in the central region (10.1) subtend an angle β_(M) of at least 40 degree and especially at least 80 degree and preferably at least 120 degree about the measuring tube axis, wherein the pole shoes are separated from one another by two gaps, wherein each gap subtends an angle γ of at least 5 degree and especially at least 10 degree and preferably at least 15 degree about the measuring tube axis.
 9. Flowmeter (1) as claimed in claim 7 or 8, wherein the guide-back part (21.4) is arranged in the central region (10.1) and has especially at least one feedthrough (21.41), especially for a measuring electrode contacting, wherein the guide-back part extends through at least one coil, and preferably through two coils, wherein especially the at least two coils are arranged on opposite sides relative to the corresponding measuring electrode.
 10. Flowmeter (1) as claimed in claim 6 or 7, wherein the pole shoes (22) subtend in the intermediate regions (10.2) about the measuring tube axis, in each case, an angle β_(Z), which is less than the angle β_(M) by at least 30 degree and especially at least 40 degree and preferably at least 50 degree, wherein the field guide-back (21.3) has on the first side and/or second side at least two guide-back parts (21.4), which magnetically connect the pole shoes, in each case, in an intermediate region.
 11. Flowmeter (1) as claimed in one of claims 6 to 10, wherein the magnet system (20) includes a shielding apparatus (23), which is adapted to minimize magnetic disturbing influences of the flanges (10.5), and collars (10.4), wherein the shielding apparatus has at least one shielding band (23.1), which at least partially surrounds the measuring tube, wherein the shielding band is arranged between a flange and the central region or on a side of the collar facing the central region, wherein the shielding band is made of a magnetically conductive material, wherein the shielding band is, for example, one piece or composed of a plurality of band portions.
 12. Flowmeter (1) as claimed in claim 11, wherein the shielding apparatus (23) has two shielding bands (23.1), each of which is associated with a flange.
 13. Flowmeter (1) as claimed in one of the previous claims 2 to 12, wherein the guide-back part (21.4) has at least 5 and especially at least 10 and preferably at least 15 plies of electrical sheet metal.
 14. Flowmeter (1) as claimed in one of the previous claims, wherein the measuring tube has an inner diameter of at least 0.35 meters and especially at least 1 meters and preferably at least 1.5 meters. 